Exhaust gas treatment devices for treating exhaust gases of automotive engines are used to effect the oxidation of carbon monoxide and hydrocarbons and the reduction of oxides of nitrogen present in the exhaust gases.
An automotive catalytic converter generally includes an outer metallic housing and a fragile catalyst support structure that is held within the outer metallic housing by a mounting mat. The mounting mat is positioned between the inner surface of the outer metallic housing and the outer surface of the fragile catalyst support structure. The fragile catalyst support structure is commonly referred to in the art as a “monolith”. The monolith may be made from a ceramic or metallic material. The mounting mat provides thermal insulation and a holding pressure sufficient for maintaining the fragile catalyst support structure in proper position during the operation of the catalytic converter.
A diesel particulate trap is used in automobiles that utilize diesel fuel. The diesel particulate trap generally includes an outer metallic housing and a fragile particulate filter structure that is held within the outer metallic housing by a mounting mat. The mounting mat is positioned between the inner surface of the housing and the outer surface of the particulate filter. Like the catalytic converter, the mat provides thermal insulation and a holding pressure for maintaining the particulate filter in proper position within the outer metallic housing during operation of the diesel particulate filter.
As noted hereinabove, the catalyst support structure of the catalytic and the diesel particulate filter are often very fragile. In fact, these structures can be so fragile that even small shockloads or stresses are often sufficient to crack or crush them. In order to protect the fragile structures from thermal and mechanical shock and other stresses noted above, as well as to provide thermal insulation and a gas seal, and to hold the fragile structures in place within the housing, it is known to position at least one ply or layer of mounting or support material within the gap between the fragile structure and the housing. Thus, the mounting mats that are positioned between the outer housing and the fragile catalyst support structure or particulate filter in the automotive exhaust gas treatment device are capable of exhibiting high temperature resistance and are capable of exerting the requisite holding pressure to maintain the catalyst support structure or particulate filter in proper position during the operation of the device.
An exhaust gas treatment device is made by wrapping the mounting mat around at least a portion of the perimeter of the fragile catalyst support structure or diesel particulate filter and locating the wrapped structure within a housing. During the wrapping of the catalyst support structure or diesel particulate filter, the mounting mat must be bent around the fragile catalyst support structure. Tensile stresses are exerted on the mounting mat which can result in cracking or tearing of the mounting mat. For intumescent mats, flaking of the vermiculite in the mat may also occur. As can be appreciated, the problem is exacerbated when heavy basis weight mounting mats are used to wrap the fragile structures or when the wrap is around a tight radius, such as for oval-shaped structures. Consequently, there is a need for a mounting mat material which is flexible and substantially crack resistant, while still providing the desired thermal insulation and holding pressure performance.